(1) Field of the Invention
The present invention relates to a data transfer apparatus used in digital broadcasting to receive content data that is repeatedly transmitted by a data broadcast, and to control transfer of the received content data.
(2) Description of the Related Art
Developments in digital broadcasting in recent years mean that it is becoming common for content data that composes data broadcast programs such as electronic program guides, weather forecasts or news to be multiplexed and broadcast, in addition to video data and audio data that compose broadcast programs.
Such content data is transmitted with a different transmission method to video and audio data. This method is called a DSM-CC (Digital Storage Media Command and Control) carousel transmission method.
This DSM-CC carousel transmission method is defined in international standard ISO/IEC 13818-6 “Part 6: Extensions for Digital Storage Media Command and Control”, and refers to a method of transmitting the same data repeatedly in cycles.
In this transmission method, the same data broadcast program is provided repeatedly to viewers, enabling each viewer to extract the content data and view the data broadcast program on demand.
Types of digital broadcasting include BS (Broadcasting Satellite) digital broadcasting and terrestrial digital broadcasting. In terrestrial digital broadcasting, various types of multiplexed data are transmitted with use of special-purpose cables from a central television station (hereinafter “key station”) to a local affiliate station (hereinafter “local station”). This enables local station to provide viewers with data broadcast programs in real time.
However, the key station and the local station generally use different data frequency bands for transmission of content data. This gives rise to a problem that when the data frequency band available to the key station is narrower than that available to the local station, if the content data from the key station is output by the local station at the same bitrate at which it is input from the key station, part of the local station's data frequency band is wasted because it is not used in output of content data. A further problem is that when the data frequency band available to the local station is narrower than the data frequency band available to the key station, content data input from the key station cannot be output at the same bitrate at which it is input.